There are two different types of image sensor packages; charge coupled device (CCD) image sensor packages and complementary metal oxide semiconductor (CMOS) image sensor packages. An image sensor packages is basically a two dimensional array of light sensing elements, and each light sensing element is corresponding to a pixel of an image captured by the image sensor package. If these image sensor packages have blemishes that obstruct or distort light, the resulting image is of bad quality. These blemishes are classified into three different types: dust, which can be removed by cleaning; scratches, which are usually long and narrow; and pits, which are usually small and more circular in nature. When these blemishes are on the light sensing elements, undesired shadows will be cast on the light sensing elements, and thus artifacts appear in the resulting image. Scratches, pits, and dust are typically created not only during the process of handling the image sensor packages, but also during the packaging process of the image sensor packages before the image sensor packages are assembled in the final product, such as a digital camera. In the past, the detection of blemishes has been done under a microscope or by viewing an image generated on a screen. These detection techniques are subjective, time consuming, and often inaccurate.
Scratches, pits, and dust will cause corrupted data in the digital image after the digital image is read from the image sensor package. To produce the highest quality image, the scratches, pits, or dusts need to be detected during the manufacturing and assembly process so that image sensor packages of bad quality can be rejected and prevented from being assembled into the final product.